replace Example

// replace element in vector; return position of new element 
int replace ( vector<int> &vect, int oldElem, int newElem ) { 
  for ( int i = 0; i < vect.size(); i++ ) {
    if (vect[i] == oldElem) { 
      vect[i] = newElem; 
      return i; 
    } 
  } 
}

// requires: vect has to have oldElem
// modified: vect
// ensures: let i be the first index such that vect @ pre[i] == oldElem
//          then, vect[i] == newElem.
//          All other elements are left unchanged.
// returns: i such that vect @ pre[i] == oldElem and vect[i] == newElem